In the processing of semiconductor substrates, or wafers, into integrated circuits (IC), gaseous plasmas are widely utilized. For example, gaseous plasmas are used to process substrates via etching, deposition, or other similar such procedures. One such plasma procedure which has found increasing application in semiconductor processing, particularly in IC fabrication such as ion implantation, sputter etching, and deposition, is a procedure which utilizes a high-density plasma source for yielding fast processing rates. High-density plasmas are desirable in the manufacturing of very large scale integrated "VLSI" and ultra large scale integrated "ULSI" circuits, having diameters up to 300 mm.
For high-density plasma processing, the substrate is positioned in a chamber on an electrically charged support base or electrode for biasing the substrate. The chamber is vacuumed to a low pressure, such as 50 mTorr or less. A process gas or work gas is then introduced into the chamber opposite the biased substrate. RF energy is inductively coupled to the gas for example, utilizing an induction coil coupled to an RF power supply. The induction coil creates a time-varying magnetic field around itself at the frequency of the applied RF energy, and the magnetic field in turn induces an electric field in the chamber. The energy from the induced electric field inside the chamber ionizes the process gas particles to form a gaseous plasma (or glow discharge) which comprises, among other particles, positively charged ions of the process gas. A negatively biased substrate collects the positively charged ion particles from the plasma to process the wafer, such as through etching or deposition. For example, the positively charged plasma ions might be attracted to the negatively biased substrate surface to bombard the surface and dislodge material particles from the substrate to thereby sputter etch a material layer from the substrate surface.
Notwithstanding the increased popularity of high-density plasma sources and their increased application to semiconductor processing, existing high-density plasma apparatus and methods have several drawbacks. For example, semiconductor wafers processed utilizing high-density plasmas are particularly sensitive to ion damage associated with the high energy of the ion particles bombarding the surface of the substrate. High-energy ions may implant into surface of the substrate to an undesirable degree or may create charge flow within the IC devices being processed on the substrate, thus damaging those devices or changing their conductive characteristics. Such ionic damage is exacerbated by the high density of the plasma. Therefore, it is desirable to reduce the damage of the substrate attributable to ionic bombardment and charging in high-density plasmas.
Another drawback of high-density plasmas is the large amount of ultraviolet (UV) radiation which is generated by the plasma. UV rays of the plasma strike the substrate and enter the oxide layers of the substrate to create charges which may migrate into the gate regions of the IC devices. Alternatively, the charges might actually be created in the gate regions of the devices by the radiation. The created charges degrade the gate regions and may change the electrical characteristics of the device. Furthermore, the undesirable UV radiation may create charges which migrate to or are located in the interfaces of the devices to create undesirable interfacial charge states which also change the electrical characteristics of the device. Still further, minority carrier action is changed by the damaging radiation which further degrades the characteristics of the IC devices and the yield from the processed substrate. Accordingly, it is desirable to reduce the effect of the damaging UV radiation, and other radiation from the high-density plasma.
As with most plasma applications, particularly plasma etching, it is desirable to control the plasma to further control the etch and direct the etch where it is required on the substrate. To that end, it is also desirable to directionalize the etch produced from high-density plasmas for advanced etching applications. Such directed or focused processing, referred to as anisotropic processing, is particularly applicable for narrow, high-aspect ratio structures which need to be etched for subsequent deposition thereon. The vertical characteristics of anisotropic etching allow deeper, cleaner etching of narrow circuit structures. Therefore, anisotropic processing for the manufacturing of VLSI and ULSI circuits is certainly a desirable feature for high-density plasma processing.
Accordingly, it is an objective of the present invention to provide low-damage processing of semiconductor materials for forming VLSI and ULSI circuits.
Another objective of the present invention is to provide a uniform, high-density plasma which may be utilized for high rate processing of VLSI and ULSI circuits without subsequent damage of the devices therein.
It is another objective of the present invention to provide a high-density, anisotropic plasma for directional etching of narrow, high aspect ratio structures on a substrate.
It is still a further objective of the present invention to utilize a high-density plasma source while reducing radiation damage of the devices on the substrate being processed.
It is a further objective of the present invention to reduce the ion damage of substrates processed utilizing high-density plasmas.